In 2009-2010, random samples of the causal agent of barley powdery mildew were collected in Daugavpils (south-eastern Latvia, Latgale region), Stende (north-western Latvia, Kurzeme region) and Priekuļi (north-eastern Latvia, Vidzeme region). Virulence frequency, complexity and pathotypes were calculated in the pathogen populations. Significant differences of virulence detected by the genes